Systems and methods for middle ear immittance testing

Abstract

Acoustic immittance and other characteristics of ears may be determined by measuring eardrum displacements resulting from application of pressure to the eardrum. For example, optical coherence tomography may be applied to monitor eardrum displacements responsive to a sound. The pressure corresponding to the sound is measured by a suitable instrument such as a microphone. The measured displacements and pressures may be processed to obtain a measure of immitance.

What is claimed is: 
     
       1. A system comprising:
 an audio source configured to deliver a sound stimulus within an ear canal for inducing motion of an eardrum at one or more frequencies; 
 a combined structural and Doppler optical coherence tomography imaging system configured to obtain structural optical coherence tomography data and Doppler optical coherence tomography data characterizing a surf ace of the eardrum, and to measure spatially resolved displacement phase and amplitude values characterizing motion of the surface of the eardrum in response to the applied sound stimulus; and 
 a processor configured to:
 process the structural optical coherence tomography data to determine local surface normal vectors associated with the surface; and 
 employ the spatially resolved displacement amplitude and phase values, the local surface normal vectors, and the one or more frequencies of the applied sound stimulus to calculate a volume velocity associated with volume displacement normal to the surface of the eardrum; 
 
 wherein the processor is further configured such that prior to calculating the volume velocity, the spatially resolved displacement amplitudes are corrected based on the respective local surface normal vectors. 
 
     
     
       2. The system according to  claim 1  wherein the volume velocity, at a given frequency, is obtained by employing the spatially resolved displacement amplitude and phase values, the local normal surface vectors and the given frequency to calculate a local velocity normal to the surface of the eardrum, and integrating the local velocity over the surface of the eardrum to obtain the volume velocity associated with the motion of the eardrum. 
     
     
       3. The system according to  claim 2  wherein the system further comprises a microphone operable to measure a pressure of the sound stimulus on the surface, and wherein the processor is further configured to process the volume velocity and the measured pressure to calculate an acoustic impedance. 
     
     
       4. The system according to  claim 3  comprising a device for applying a quasi-static pressure to the ear canal and an earpiece that creates an acoustic seal with the ear canal wherein the system is configured to report a change in the volume velocity or acoustic impedance as the quasi-static pressure is varied. 
     
     
       5. The system according to  claim 3  wherein the audio source is configured such that the sound stimulus is operative to elicit an acoustic reflex response, and wherein the system is configured to measure a change in the acoustic impedance resulting from the acoustic reflex response. 
     
     
       6. The system according to  claim 3  wherein the system is configured to monitor a decay in an acoustic impedance change caused by the acoustic reflex over time. 
     
     
       7. The system according to  claim 3  wherein the processor is further configured such that, prior to calculating the acoustic impedance, the following operations are performed:
 processing image data collected by the optical coherence imaging system to determine a fraction of the eardrum that has been obscured during image acquisition; and 
 employing the fraction to scale the measured volume velocity to compensate for the obscured fraction of the eardrum. 
 
     
     
       8. The system according to  claim 2  wherein the audio source is configured such that the sound stimulus is operative to elicit an acoustic reflex response, the system configured to measure motion of at least one of a malleus, incus, stapes and stapedius tendon when the acoustic reflex response is active. 
     
     
       9. The system according to  claim 5  wherein the sound stimulus is sinusoidal. 
     
     
       10. The system according to  claim 5  wherein the sound stimulus is a broadband stimulus. 
     
     
       11. The system according to  claim 10  wherein the broadband stimulus comprises one of clicks, white noise and signals comprising a sum of sine waves at multiple frequencies. 
     
     
       12. The system according to  claim 1  comprising a pump controllably coupled to the processor, the pump configured to maintain a static pressure in the ear canal. 
     
     
       13. The system according to  claim 1  wherein the optical coherence tomography imaging system comprises one of a swept-source laser and a broadband light source. 
     
     
       14. The system according to  claim 13  wherein the swept-source laser is synchronized with a sweep clock signal, the sweep clock signal synchronizing the laser with an acoustic phase of the sound stimulus. 
     
     
       15. The system according to  claim 1  wherein the processor is configured to process signals from an interferometer to produce an interferogram representing one or both the ear canal and the surface. 
     
     
       16. The system according to  claim 15  wherein the processor is configured to extract structural optical coherence tomography data from a computed magnitude of a discrete Fourier transform of the interferogram. 
     
     
       17. The system according to  claim 16  wherein the processor is configured to extract Doppler optical coherence tomography data from the interferogram. 
     
     
       18. The system according to  claim 1  wherein the processor is configured to calculate the volume velocity by:
 determining a plurality of voxels lying on the surface using the structural optical coherence tomography data; 
 employing the structural optical coherence tomography data to determine a local surface normal vector for each voxel; 
 determining vibration displacement amplitude and phase for each of the plurality of voxels using the Doppler optical coherence tomography data; 
 employing the vibration displacement amplitude, phase and the local surface normal vector of each voxel to determine a plurality of spatially resolved individual velocities normal to the surface, each of the plurality of individual velocities corresponding to an individual velocity of one of the plurality of voxels normal to the surface, induced by the sound stimulus; and 
 integrating over the plurality of spatially resolved individual velocities. 
 
     
     
       19. The system according to  claim 18  wherein the plurality of voxels corresponds to a portion of the surface that includes an umbo at which a tympanic membrane is coupled to an ossicular chain of an ear. 
     
     
       20. A system for measuring an acoustic impedance of a middle ear of an ear, the system comprising:
 an audio source operable to generate a sound stimulus, the sound stimulus effective to induce motion of an eardrum of the ear at one or more frequencies; 
 a combined structural and Doppler optical coherence tomography imaging system configured to obtain structural optical coherence tomography data characterizing a surface of the eardrum, and to measure displacement amplitude and phase values at points of a two-dimensional array of points on the eardrum in response to the sound stimulus; 
 a microphone operable to measure pressure of the sound stimulus on the ear drum; and 
 a processor, the processor configured to:
 process the structural optical coherence tomography to determine local surface normal vectors associated with the surface; and 
 employ the displacement amplitude and phase values, the local surface normal vectors, and the one or more frequencies of the applied sound stimulus to calculate a volume velocity associated with volume displacement normal to the surface of the eardrum; and 
 calculate the acoustic impedance of the middle ear as a ratio of the measured pressure of the sound stimulus on the ear drum to the volume velocity; 
 wherein the processor is further configured such that prior to calculating the volume velocity, the spatially resolved displacement amplitudes are corrected based on the local surface normal vectors. 
 
 
     
     
       21. A method comprising:
 inducing motion of an eardrum by applying a sound stimulus to the eardrum at one or more frequencies; 
 with a combined structural and Doppler optical coherence tomography imaging system, imaging a surface of the eardrum to obtain structural optical coherence tomography data characterizing a surface of the eardrum and measure spatially-resolved displacement phase and amplitude values characterizing motion of the surface of the eardrum in response to the applied sound stimulus; and 
 by an electronic data processor, processing the structural optical coherence tomography to determine local surface normal vectors associated with the surface and employing the spatially resolved displacement amplitude and phase values, the local surface normal vectors, and the one or more frequencies of the applied sound stimulus to calculate a volume velocity associated with volume displacement normal to the surface of the eardrum; 
 wherein, prior to calculating the volume velocity, the spatially resolved displacement amplitudes are corrected based on the respective local surface normal vectors. 
 
     
     
       22. The method according to  claim 21  wherein the system further comprises a microphone operable to measure a pressure of the sound stimulus on the surface, and wherein the processor is further configured to process the volume velocity and the measured pressure to calculate an acoustic impedance. 
     
     
       23. The method according to  claim 22  further comprising, prior to calculating the acoustic impedance, performing the following steps:
 processing image data collected by the optical coherence imaging system to determine a fraction of the eardrum that has been obscured during image acquisition; and 
 employing the fraction to scale the measured volume velocity to compensate for the obscured fraction of the eardrum.